Measurement of Neutrino Oscillation with KamLAND: Evidence of Spectral Distortion

258 observed $\bar\nu_e -> \bar\nu_e$ events

expected events without oscillations

expected background events

disappearance confirmed at 99.998% C.L.

energy spectrum shows distorsions with 99.6% C.L.

best-fit of KamLAND data: $\Delta{m}^2 = 7.9 {}^{+0.6}_{-0.5} \times 10^{-5} \mathrm{eV}^2$

best-fit of KamLAND + solar data: $\Delta{m}^2 = 7.9 {}^{+0.6}_{-0.5} \times 10^{-5} \mathrm{eV}^2$ , $\tan^2\theta = 0.40 {}^{+0.10}_{-0.07}$

Prompt event energy spectrum of $\bar\nu_e$ candidate events with associated background spectra. The shaded band indicates the systematic error in the best-fit reactor spectrum above 2.6 MeV.

Ratio of the observed anti-neutrino spectrum to the expectation for no-oscillation versus $\mathrm{L}_{0}/\mathrm{E}$ . The curves show the expectation for the best-fit oscillation, best-fit decay and best-fit decoherence models taking into account the individual time-dependent flux variations of all reactors and detector effects. The data points and models are plotted with $\mathrm{L}_{0}=180\mathrm{km}$ , as if all anti-neutrinos detected in KamLAND were due to a single reactor at this distance.

Neutrino oscillation parameter allowed region from KamLAND anti-neutrino data (shaded regions) and solar neutrino experiments (lines) [nucl-ex/0309004].

Result of a combined two-neutrino oscillation analysis of KamLAND and the observed solar neutrino fluxes under the assumption of CPT invariance. The fit gives $\Delta{m}^2 = 7.9 {}^{+0.6}_{-0.5} \times 10^{-5} \mathrm{eV}^2$ and $\tan^2\theta = 0.40 {}^{+0.10}_{-0.07}$ including the allowed 1-sigma parameter range.

258 observed $\bar\nu_e -> \bar\nu_e$ events

expected events without oscillations

expected background events

disappearance confirmed at 99.995% C.L.

energy spectrum shows distorsions with 99.9% C.L.

best-fit of KamLAND data: $\Delta{m}^2 = 8.3 \times 10^{-5} \mathrm{eV}^2$ , $\tan^2\theta = 0.41$

best-fit of KamLAND + solar data: $\Delta{m}^2 = 8.2 {}^{+0.6}_{-0.5} \times 10^{-5} \mathrm{eV}^2$ , $\tan^2\theta = 0.40 {}^{+0.09}_{-0.07}$

Prompt event energy spectrum of the $\bar\nu_e$ candidate events along with the spectrum of accidental backgrounds. The shaded band indicates the systematic error in the best-fit reactor spectrum above 2.6 MeV.

Allowed regions of neutrino oscillation parameters from KamLAND anti-neutrino data (shaded regions) and solar neutrino experiments (lines) [nucl-ex/0309004].

Result of a combined two-neutrino oscillation analysis of KamLAND and the observed solar neutrino fluxes under the assumption of CPT invariance. The best-fit point is $\Delta{m}^2 = 8.2 {}^{+0.6}_{-0.5} \times 10^{-5} \mathrm{eV}^2$ and $\tan^2\theta = 0.40 {}^{+0.09}_{-0.07}$ including the allowed 1-sigma parameter range.